Initiator injection molding

However, it is moisture absorption that gives nylon its toughness. Upon initial injection molding manufactured nylon profiles are typically very hard and brittle. After they left to cure, they absorb moisture from the air and become very impact resistant. The curing (or softening ) period for nylon profiles takes 2-3 weeks. Clearly, at outdoors conditions it usually takes much less time. 

Several injection-molded polycarbonate (PC) disks used in a consumer product (i.e., a clock face) were analyzed, because the disks contained defects. The defects were analyzed initially and imaged using a stereoscopic microscope fitted with a digital camera. The defects present on the samples were easily identified. It was noticed that the defects were located on different regions of the molded part. This important observation eliminated a systematic problem or an imperfection at a specific site on the mold surface as the cause of the defect. 

Poly vinylidene fluoride is polymerized under pressure at 25-150°C in an emulsion using a fluorinated surfactant to minimize chain transfer with the emulsifying agent. Ammonium persulfate is used as the initiator. The homopolymer is highly crystalline and melts at 170°C. It can be injection molded to produce articles with a tensile strength of 7000 psi (48 MPal. a modulus of elasticity in tension of 1.2 x 105 psi and a heat deflection of 3003F (149°C). 

Most real cases of polymer melting (and solidification) involve complex geometries and shapes, temperature-dependent properties, and a phase change. The rigorous treatment for such problems involve numerical solutions (12-15) using finite difference (FDM) or FEMs. Figure 5.9 presents calculated temperature profiles using the Crank-Nicolson FDM (16) for the solidification of a HDPE melt inside a flat-sheet injection-mold cavity. The HDPE melt that has filled the cavity is considered to be initially isothermal at 300°F, and the mold wall temperature is 100°F. 

Fig. 13.16 Schematic representation of the flow pattern in the advancing front between two parallel cold walls. Black rectangles denote the stretching and orientation of a fluid particle approaching the central region of the front. The curved shape of the front causes fluid particles initially oriented in the y direction to end up on the wall, oriented in the x direction. The velocity profile upstream from the front is in the x direction and is viewed from a coordinate system located on the front. [Reprinted by permission from Z. Tadmor Molecular Orientation in Injection Molding, J. Appl. Polym. Sci., 18, 1753 (1974).]...

Aqueous suspension polymerization requires the usual additives, such as free radical initiators, colloidal dispersants (not always), and chain transfer agents to control molecular weight. After the process is completed, the suspension contains spherical particles approximately 100 pm in diameter. Suspension polymers are available as free-flowing powder or in pellet form for extrusion or injection molding.58... 

Vinylene carbonate is one of the few 1,2-disubstituted ethylenes that is known to undergo facile radical initiated homopolymerization. Initiation may be by oxygen, peroxides or cobalt-60 y-radiation. Such polymers are reportedly useful as coatings and films. Vinylene carbonate also copolymerizes with ethylene under high pressure to yield a material with about 10% vinylene carbonate content. This polymer, when blended with polyvinyl chloride, is suitable for injection molding. 

This is an important area that has to be thoroughly analyzed and studied to obtain the desired performance of the complete line and/or its parts such as the injection mold, extruder puller, and so on. The first task is to determine what is required and how to approach any potential problem. Adequate PC and its associated instrumentation are essential for product control. Sometimes the goal is precise adherence to a control point, other times it is sufficient to maintain a control within a comparatively narrow range. For effortless controller tuning and lowest initial and operating cost, the processor should select the simplest controller (temperature, time, pressure, flow rate, etc. that will produce the desired results. For the complete line, they can range from unsophisticated to extremely sophisticated devices that interrelate information. As an example there is the computer Hosokawa Alpine... 

---